Nigeria's Diezani Alison-Madueke, Minister of Petroleum Resources and Alternate President of the OPEC Conference speaks to journalistsGetty

Money belonging to former Nigeria oil minister Diezani Alison-Madueke has been seized following her arrest in London on 2 October. The ex-petroleum minister, who was in the role between 2010 and 2015, was apprehended with four other people by the National Crime Agency (NCA) for suspected bribery and money laundering offences.

She was later released on bail - although the amount is not yet clear - the same evening, while £27,000 found on her was seized and will be held until April 2016. Nigeria's financial crimes unit sealed one of Alison-Madueke's houses in the federal capital Abuja on the night of her arrest, according to Reuters.

The NCA refused to disclose the identity of those arrested. A spokesperson for the agency told IBTimes UK: "We only confirm names when we charge people. The people who were arrested last Friday were bailed by the court and have not been charged yet, so we have not confirmed any name. All the information that we are able to make public are on our website." However, Alison-Madueke's arrest was confirmed by her family.

The NCA also said in a statement on its website that investigations on alleged bribery and money laundering had started in 2013 "under the Proceeds of Corruption Unit, and transferred to the NCA earlier in 2015". The agency also told Nigerian newspaper The Guardian that it has not "scheduled any charges".

The Nigerian government said in a statement that it was aware of the arrest. It added: "All the investigative agencies are working very closely with the British law enforcement. Nigerian authorities are saying for the first time that matters are being handled with seriousness and deep commitment. Nobody wants to give the impression that this government is frivolous and unserious."

When contacted by IBTimes UK, Femi Adesina, the spokesperson for Muhammadu Buhari, said the Nigerian president had no comments regarding the case. However, the state house released a statement days after the arrest in which Buhari congratulated the UK and Switzerland for their efforts to repatriate stolen funds belonging to Nigeria.

Alison-Madueke, who became the first female president of the Organization of the Petroleum Exporting Countries (Opec) in 2014, was arrested days after Buhari appointed himself as the country's oil minister, after he vowed he would recover millions of dollars worth of funds he alleged were stolen during previous administrations.

The leader also alleged some 250,000 barrels of Nigerian crude oil are stolen every day and sold to other countries at higher prices. In order to stop illicit activities in the oil industry, Buhari replaced the whole board of the state-run Nigerian National Petroleum Corporation (NNPC) and temporarily banned some 113 vessels from taking crude oil from Nigerian ports.

While Alison-Madueke was in office, former governor of Nigeria Central Bank Sanusi Lamido Sanusi was suspended after he claimed $20bn (£12bn) of oil revenue "went missing" from state oil company Nigerian National Petroleum Corporation (NNPC).

According to the Premium Times, Alison-Madueke – who has been dubbed "one of the most powerful officials of President Goodluck Jonathan" – admitted to spending $3.5bn (£2.3bn) of Nigeria's money without budgetary approval in February 2014.

During her time in the role, she supported the unpopular attempt by Jonathan in 2012 to end fuel subsidies, arguing it posed a financial burden on the government's finances. The government backtracked on its decision following rallies that caused at least 16 deaths.